Radio shielded spark plug and the like



T. TOGNOLA RADIO SHIELDED SPARK PLUG AND THE LIKE Filed March 22, 1940Nov. 3, 1942.

Fig 2 INVENTOR ATTORNEY Patented Nov. 3, 1942 2,300,714 rumro summonsmirk-two AND rnnmxnq:

Tullio Tognola, Sidney, N. Y., assl gnor to Bendix Aviation Corporation,South Bend, Ind., a corporation of Delaware Application March 22, 194 0,Serial No. 325,286

8 Claims.

This invention relates to radio-shielding means for electricalconductors, and more particularly to radio-shielding conduits for hightension ignition conductors, such as at the spark plug of an internalcombustion engine.

In radio-shielding means heretofore provided for the ignition leads tothe spark plugs of an internal combustion engine, for example, muchdifficulty has been continuously experienced in providing connectingshielding units which may be readily assembled and disassembled withoutdanger of damaging insulation within the same and also provide adequateshielding to prevent interference with radio reception and adequateprotection against the entrance of moisture under severe operatingconditions, such as high speed flying in rain.

It is accordingly one of the objects of the present invention to providenovel means particularly adapted for use in shielded spark plugs of thetype now in common use whereby the foregoing difficulties may beobviated.

Another object of the invention is to provide novel means in a shieldedspark plug whereby the insulation within the shielding barrel thereof isprotected against damage and whereby a firm seat having a comparativelylarge flat surface is provided for engagement by the connectingshielding conduit to thereby obviate the entrance of moisture andprovide a good electrical connection between the connecting parts of theshield.

a shielded spark plug 8, but it will be understood that the inventionmay be employed at other points in a radio-shielding system, such as atthe connection between a shielding conduit and the shielding manifold ofa radio-shielding harness for the ignition system of an engine.Generally speaking, spark plug 6 may be of a type wellknown in the artwhich comprises a shell 1 adapted to threadedly engage an opening in aninternal combustion engine cylinder (not shown). Threaded into shell Ior otherwise secured thereto is a nut 8 which has an upwardly extendingtube or barrel 9 that is lined with electrical insulating material l0,such as rolled sheet mica. Supported by nut 8 and insulated therefrom inany well-known manner, such as by means including stacks of mica washersH and mica sleeve [2, is a center electrode I3, the lower enlarged endl4 of which is in cooperative relation with a ground electrode l5secured in shell I.

For the purpose of protecting the upper end of insulating sleeve orlining I0 from damage during insertion and removal of a conductor to andfrom barrel 9 for connecting center electrode l3 with a source of hightension current (not shown) a number of expedients have heretofore beenemployed but none has been completely successful. In some instances, forexample, the outer end of the spark plug barrel has been made thin androlled inwardly to form a protecting flange. In

' other instances, the end of the insulating sleeve The above andfurther objects and novel features of the invention will more fullyappear from the following detailed description when the same is read inconnection with the accompanying drawing. It is to be expresslyunderstood, how ever, that the drawing is for the purpose ofillustration only and is not intended to define the limits of theinvention, reference for this latter purpose being had primarily to theappended claims.

In the drawing, wherein like reference characters refer tolike partsthroughout the several views:

Fig. 1 is a side elevation, partly in section and with parts brokenaway, of a shielded spark plug and associated shielding conduitembodying one form of the invention; and,

Fig. 2 is a detail view, partly in section and with parts broken away,showing a portion of the upper end of the spark plug barrel on anenlarged scale.

The single embodiment of the invention illustrated in the drawing isshown, by way of exrule or the like.

has been bound either separately or together with the end of the barrelby means of a metallic fer- Also, split rings have been removablyinserted in the upper end of the barrel as a protecting means. All ofthese methods or structures possess disadvantages which are wellknown tothose skilled in the art.

In order to obviate the disadvantages of prior structures of the abovecharacter, the present invention comprehends associating a rigidmetallic ring IS with barrel 9 in a novel manner. In the form shown,barrel 9 is provided with an enlarged bore at the outer end thereof toform an internal shoulder l'l. Ring I6 is formed to fit snugly into saidenlarged bore and seat against shoulder ll, the inner diameter of saidring being equal to or preferably slightly less than the internaldiameter of insulating lining Hi. In radial cross-section, ring I8 issubstantially rectangular, except that the upper outside corner thereofis beveled or chamfered, as at l8. The outer end of barrel 9 is rolledor staked inwardly into contact with the beveled surface [8 to form anannular tongue ample, in connection with the shielding barrel of I9adaptedto secure ring IS in position. After the end of barrel 9 is spunor pressed inwardly, both the barrel and the ring are machined so thattongue I! and the outer face of the ring together form a flat annularseat 20 of substantial radial width--a metallic seat which is firm andnot subject to being damaged by bending or otherwise. The machining alsoeliminates any rough edges resulting from the spinning-in oper-- ation.

For connecting center electrode l3 to a source of high tension currentthere is provided an insulated conductor 2| which extends through aflexible metallic conduit 22. The end of conduit 22 has a ferrule 23secured thereto, said ferrule having an external flange 24 adapted toengage seat 20. The projecting end of cable 2| is preferably surroundedby a rigid insulating spacer sleeve 25 which is adapted to slidablyextend into barrel 9. One end of sleeve 25 abuts against conduit 22, 23and is secured at its other end, in any well-known manner, to conductor2i. Surrounding conduit 22 is an internally threaded nut 26 having aninternal flange 21 adapted to engage flange 24, whereby said conduit maybe removably secured to barrel 9 to form a continuous shield for theignition conductor 2|. The threads in nut 26 engage external threads onbarrel 9 and constitute means whereby flange 24 may be pressed and heldfirmly against seat 20 to thereby form an excellent water-tight jointhaving relatively large engaging surfaces and to establish a goodelectrical connection between the parts 23 and 9 of the shielding means.

There is thus provided novel radio shielding means particularly adaptedfor use in connection with a shielded spark plug whereby the probabilityof damage to the insulating lining in the spark plug barrel or othershielding conduit is reduced to a minimum. Additionally, novel means areprovided whereby a water-tight joint is insured between the connectedparts of a shielded conduit without decreasing the effectiveness of theelectrical connection therebetween. The novel structure provided alsolends itself to ready reconditioning of the plug with which it isassociated. The invention is simple in construction and may be readilyand inexpensively incorporated in shielded spark plugs and othershielding units of the character now in almost universal use onaircraft.

Although only a single embodiment of the invention has been illustratedand described in detail, it is to be expressly understood that the sameis not limited thereto but that various changes may be made,particularly in the size, shape and composition of parts illustrated anddescribed, without departing from the spirit and scope of the inventionas the same will now be understood by those skilled in the art. Forexample, a gasket of soft metal or other suitable material may beinserted between flange 24 and seat 20, if desired. For a definition ofthe limits of the invention, reference is had primarily to the appendedclaims.

What is claimed is:

1. The combination of a rigid metallic shielding barrel having anenlarged bore at one end thereof, a comparatively thin lining ofelectrical insulating material in the normal bore of said barrel, and arigid metallic ring having a smooth outer peripheral surface and abeveled corner tightly fitted into said enlarged bore and engaging anannular shoulder in said barrel, the internal diameter of said ringbeing substantially insulating material in the normal bore of said Ibarrel, and a rigid metallic ring having a smooth outer peripheralsurface and a beveled corner tightly fitted into said enlarged bore andengaging an annular shoulder in said barrel, the internal diameter ofsaid ring being approximately equal to the internal diameter of saidlining, and the edge of said barrel being pressed inwardly around theentire periphery thereof to form a lip engaging said beveled corner andhaving a radially extending flat surface flush with the outer face ofsaid ring to form a seat, a metallic shielding conduit having anexternal flange thereon adapted to engage said seat, and a coupling nuthaving threaded engagement with said barrel and having an internalflange engaging said firstnamed flange whereby the latter is held infirm engagement with said seat.

3. Radio-shielding means for electrical conductors comprising a rigidmetallic conduit having an internal shoulder adjacent one end thereof, arelatively thin insulating sleeve in said conduit terminating adjacentsaid shoulder, and a rigid metallic ring having a smooth externalperipheral surface tightly fitted into the bore of said conduit againstsaid shoulder, the internal diameter of said ring being approximatelyequal to the internal diameter of said lining and the edge of saidconduit being pressed inwardly entirely around the periphery thereofinto engagement with said ring, said inwardly pressed edge having asurface forming a continuation of the corresponding surface of saidring.

4. The combination of a rigid metallic shielding barrel having aninternal shoulder adjacent one end thereof, a relatively thin insulatinglining in said barrel terminating adjacent the plane of said shoulder,and a rigid metallic ring having a smooth external surface tightlyfitted in said barrel in engagement with said shoulder, said ring havingan inner diameter which is approximately equal to the inner diameter ofsaid lining and the outermost edge of said barrel being pressed inwardlyto form a lip for permanently securing said ring in position in thebarrel.

5. Radio-shielding means for electrical conductors comprising a rigidmetallic conduit having an enlarged bore at one end thereof, a rigidmetallic ring having a smooth external periphery tightly fitted in saidenlarged bore against an annular shoulder in said conduit, said ringhaving a smaller internal diameter than the diameter of the normal boreof said conduit, and means for securing said ring in said enlarged bore.

6. Radio-shielding means for electrical conductors comprising a rigidmetallic conduit having an internal shoulder adjacent one end thereofand a rigid metallic ring having a smooth outer periphery fitted andsecured in the bore of said conduit against said shoulder, the edge ofsaid conduit having a flat surface in the plane of the outer flatsurface of said ring, said flat surfaces forming a continuous annularplane surface.

7. A radio shielded spark plug comprising a shell, a tubular metallicshielding barrel secured to said shell and surrounding and projectingbeyond the upwardly extending portion of said electrode, said barrelhaving an enlarged bore forming an internal shoulder adjacent the outerend thereof, a relatively thin lining of insulating material in saidbarrel terminating adjacent the plane of said shoulder, and a rigidmetallic ring having a smooth external peripheral surface secured insaid enlarged bore and engaging said shoulder, the inner diameter 01'said ring being approximately equal to the inner diameter of said liningand the upper face of said ring being flush with the end of said barrelto form therewith a relatively wide annular seating surface.

8. A radio shielded spark plug comprising a tubular metallic shell, 9.center electrode assembly comprising a center electrode and insulatingmeans therefor mounted in said shell and extending upwardly therefrom, atubular metallic shielding barrel secured to said shell around saidupwardly extending portion of said assembly, said barrel projectingbeyond said assembly to form a socket and having an enlarged boreforming an internal shoulder adjacent the outer end thereof, arelatively thin lining of insulating material in said barrel terminatingadjacent the plane of said shoulder, a rigid metallic ring having asmooth external peripheral surface and a beveled corner seated in saidenlarged bore in engagement with said shoulder, the internal diameter ofsaid ring being approximately equal to the internal diameter of saidlining and the edge of said barrel being pressed inwardly around theentire periphery thereof to form a lip engaglng said beveled corner andhaving a radially extending fiat surface flush with the upper surface ofsaid ring to form a. relatively wide annular seating surface.

TUILIO TOGNOLA.

